1. Field of the Invention
The present invention relates to the use of hot melt adhesive in the construction of reclosable packages having a high burst zipper.
2. Description of the Prior Art
Hot melt adhesives have a long history of use in the packaging industry, as well as many other industries. In particular, these adhesives are particularly adaptable to use in large bag applications, such as those used for pet food, charcoal, kitty litter, rice, etc. Typical construction of these packages or bags includes lap seams, pinch bottom seals, and zipper reclosures that are all sealed by hot melt adhesives.
EVA-based non-cross-linkable hot melt adhesives have been used for years, because they are easy to apply, and they set up quickly, allowing for line speed efficiency. While they are an industry standard, they do not have the ability to withstand a hot load test, where the glue seam is subject to a load under high heat environments, such as described previously in application Ser. No. 11/728,477 entitled “High Burst Zipper Assembly for Reclosable Packages”; application Ser. No. 11/728,405 entitled “Method of Producing High Burst Zipper Assemblies for Large Reclosable Packages”; and application Ser. No. 11/728,413 entitled “Hot Melt Adhesive Systems for Zipper Assemblies on Large Bag Constructions of Various Substrates”, all filed on Mar. 26, 2007, and all hereby incorporated by reference. The reactive, cross-linkable hot melts described therein can withstand the rigors of the hot load test, but they do not have the initial strength or hot tack of the EVA based hot melts. In this case, hot tack refers to the ability of the glue seam to immediately be able to withstand a shearing force on the seam without the substrates creeping under the shear load. The high initial strength or hot tack is particularly important for preventing the thickness of the bag from prying the glue joint open at the flanges and for maintaining high production rates and speeds during manufacture. A similar reclosable package is disclosed in U.S. Pat. No. 6,354,738 entitled “Tamper Evident Reclosable Plastic Bag” issued to Buckman on Mar. 12, 2002.
In short, EVA-based and polyamide-based non-cross-linkable adhesives have generally had good hot tack performance but poor hot load performance, while reactive, cross-linkable adhesives have had fair hot tack performance but excellent hot load performance.